Sort NSmutableArray that contains 2 types of object?

Question

I have an NSMutableArray that contains 2 types of Objects.

Both objects contain a field for dates (date Strings with different formats) with different names.

What's the best and fastest way to sort them all based on the date? Is it possible to use an NSSortDescriptor in this situation?

Answer 1

If you are targeting Mac OS X v10.6 or iOS4 and higher you can sort using comparator similar to this

NSDateFormatter *formatter1 = ...; //create and configure date formatter for Class1
NSDateFormatter *formatter2 = ...; //create and configure date formatter for Class2


[arrayOfObjects sortUsingComparator:^NSComparisonResult(id obj1, id obj2) {
    NSDate *date1 = nil, *date2 = nil;
    //Get first objects date
    if([obj1 isKindOfClass:[Class1 class]])
    {
        date1 = [formatter1 dateFromString:[obj1 class1Date]];
    }
    else if([obj1 isKindOfClass:[Class2 class]])
    {
        date1 = [formatter2 dateFromString:[obj1 class2Date]];
    }

    //Get second objects date
    if([obj2 isKindOfClass:[Class1 class]])
    {
        date2 = [formatter1 dateFromString:[obj2 class1Date]];
    }
    else if([obj2 isKindOfClass:[Class2 class]])
    {
        date2 = [formatter2 dateFromString:[obj2 class2Date]];
    }

    NSAssert(date1 != nil, @"Could not parse date from %@", obj1);
    NSAssert(date2 != nil, @"Could not parse date from %@", obj2);

    return [date1 compare:date2];
}];

Besides checking for the class you could also check if it responds to selector.

Answer 2

You could add a category to unify the date field name. Let's say class A's instances have a field "dateString" and class B's instances have a field "creationDateString"... You could do this:

@implementation A (SortByDate)

-(NSDate*)sortDate
{
    static NSDateFormatter * formatter = nil ;
    static dispatch_once_t once = 0 ;
    dispatch_once( & once, ^{ formatter = ... } ) ;

    return [ formatter dateFromString:self.dateString ] ;
}
@end

@implementation B (SortByDate)
-(NSDate*)sortDate
{
    static NSDateFormatter * formatter = nil ;
    static dispatch_once_t once = 0 ;
    dispatch_once( & once, ^{ formatter = ... } ) ;

    return [ formatter dateFromString:self.creationDateString ] ;
}
@end

Now you can sort all objects in your array by their sortDate property:

NSArray * sortedByDateArray = [ unsortedArray sortedArrayUsingComparator:^( id a, id b ){
    return [ [ a sortDate ] compare:[ b sortDate ] ] ;
}];

EDIT Or with a sort descriptor:

NSArray * sortedArray = [ unsortedArray sortedArrayUsingDescriptors:[ NSArray arrayWithObject:[ NSSortDescriptor sortDescriptorWithKey:@"sortDate" ascending:YES ] ] ] ;